Implantable medical devices (IMDs), including pacemakers and cardioverter-defibrillators (ICDs), record cardiac electrogram (EGM) signals for detecting the heart rhythm and responding as needed with pacing therapy or high-voltage cardioversion/defibrillation therapy. Episodes of the EGM signals are typically stored in the memory of the IMD, particularly when a tachyarrhythmia is detected by the IMD. Reviewing episode data stored in the IMD by a clinician provides the clinician with valuable information for diagnosing the patient's condition and selecting the best treatment options for the patient. To enable the clinician to efficiently identify electrical events on the EGM signal as they are sensed by the IMD, a Marker Channel® (Medtronic, Inc., Minneapolis Minn.) can be displayed to provide indentifying event markers and corresponding annotation of events occurring during stored episodes of EGM data. The Marker Channel data may be transmitted from the IMD to an external interrogating programmer through wireless telemetric communication. The event identification markers and corresponding annotation identify various events as interpreted by the IMD are displayed by the programmer. Events identified and displayed may include atrial sense events (AS), atrial pace events (AP), ventricular sense events (VS), and ventricular pacing events (VP), and refractory sense events (VSR or ASR).
In some cases undersensing or oversensing of cardiac events on the EGM signal occurs. On an atrial sensing channel, P-waves may be undersensed or far field R-waves (FFRWs) may be oversensed leading to erroneous cardiac interval measurements and heart rate detection. On the ventricular sensing channel, undersensing of R-waves or oversensing of T-waves can occur. Oversensing of non-cardiac noise can also occur. In a Marker Channel display, the sensed events are displayed and labeled as “seen” by the IMD. As such, a clinician or other user reviewing an episode will see the Marker Channel events as sensed by the IMD, which may omit undersensed events and include oversensed events labeled as AS or VS events. In this situation, the clinician is presented with inaccurate event rates and patterns, limiting the ability to efficiently and accurately identify the patterns and rhythms actually presented by the patient without careful manual analysis of the EGM signal itself.